The Nearctic northern goshawk (Accipiter gentilis atricapillis) is a resident of conifer, broadleaf, and mixed forests from the boreal to the southwestern montane regions of North America. We report on a 20‐year mark‐recapture investigation (1991–2010) of the distribution and density of breeders, temporal and spatial variability in breeding, nestling sex ratios, local versus immigrant recruitment of breeders, breeding age structure, age‐specific survival rates, and rate of population change (λ) of this species on the Kaibab Plateau, a forested sky island in northern Arizona, USA. We used an information‐theoretic approach to rank models representing alternative hypotheses about the influence of annual fluctuations in precipitation on the annual frequency of goshawk breeding and fledgling production. We studied 125 goshawk breeding territories, representing approximately 87% of an estimated 144 total territories based on a mean distance of 3.8 km between territory centers in a 1,728‐km² study area. The salient demographic feature of the population was extensive annual variation in breeding, which manifested as large inter‐annual variation in proportions of pairs laying eggs, brood sizes, nest failure rates, and fledgling production. The percent of territories known in a prior year in which eggs were laid in a current year ranged from 8% to 86% ( = 37%, SE = 4.51), annual mean nest failure rate (active nests that failed) ranged from 12% to 48% (overall  = 23%, SE = 2.48), and mean annual brood size of successful nests (fledged ≥1 fledgling) ranged from 1.5 young to 2.5 young (overall  = 2.0 young, SE = 0.03). Inter‐annual variation in reproduction closely tracked inter‐annual variation in precipitation, which we hypothesize influenced primary forest productivity and bird and mammal prey abundance. The best breeding years (1992–1993, 77–87% of pairs laid eggs) were coincident with a record‐long El Niño‐Southern Oscillation (ENSO) wet period and the worst breeding year (2003; 8% of pairs laid eggs) was the last of a 3‐year record drought. Overall breeding success was 83% with most failures occurring during incubation; once eggs hatched, goshawks tended to fledge young. The pooled 20‐year nestling sex ratio did not differ from unity (53% M; n = 410 M, 366 F) but was significantly male‐biased in 2 years and female‐biased in 1 year. Nonetheless, the overall greater production of male fledglings followed a strong trend of greater male production in other goshawk populations, suggesting that breeders might have been adaptively adjusting their offspring sex ratio, perhaps to produce more of the rarer (male) sex. Annual recruitment of new individuals into the breeding population averaged 43% during the study. Study area recruitment rate of hawks locally born (in situ) and banded was 0.12. Both sexes had equal tendencies to return to the Kaibab Plateau to breed (no differences in philopatry) and there were no differences in natal dispersal distances (natal to first breeding site) between the sexes. During the final years of study (1999–2010), an estimated 46% of breeding recruits were locally born and 54% were immigrants from distant forests. Minimum age at first breeding was 2 years and mean age at first breeding by known‐age hawks (banded as nestlings or aged on plumage at first breeding) was 3.7 years for males and 3.5 years for females. Mean lifespan (yr from first banding as nestling to last resighting) of known‐age goshawks was 6.9 years for both sexes. Mean minimum apparent lifespan of breeders aged ≥4 years based on plumage at first capture was 6.5 years for both sexes. Average age of goshawks at their first detection was 3.9 years old, at which time apparent survival was estimated at 0.77 for both sexes, which was just slightly less than the peak survival of 0.78 as a function of age. Age‐specific survival estimates showed a steady decline after 9 years old and approached 0 at 20 years of age. Estimates of λ for breeding adults (M, 0.94, SE = 0.037; F, 0.98, SE = 0.038) provided only weak evidence for a population decline during the study. Although sex was not in the top survival model, models including age + sex were competitive, evidencing lower male than female survival, a finding corroborated by the occurrence of sex effects in the top λ model. Lower male survival may result from higher mortality associated with hunting agile prey in vegetation‐filled environments during long breeding seasons when they are the primary forager. Lower survival may be compensated by the more frequent production (53%) of male fledglings. High‐severity crown fire was an existential threat to the population. In addition to 4 large high‐severity fires that burned roughly 3,770 ha (equal to 3 goshawk territories) in the 30 years preceding 1991, 6 high‐severity fires burned another 30,945 ha during our study and killed most (>64%) of the forests in 8 known territories and possibly another 2 that were burned before we completed surveys.

中文翻译：

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可变环境中北部苍鹰的长期人口统计学

Nearctic北部苍鹰（Accipiter gentilis atricapillis）是北美洲北部至西北山区的针叶树，阔叶林和混交林的居民。我们报告了一项为期20年的标记夺回调查（1991-2010），涉及繁殖者的分布和密度，繁殖的时空变化，雏鸟性别比，繁殖者的本地招募与移民招募，繁殖年龄结构，按年龄段生存率和种群变化率（λ）在美国亚利桑那州北部森林繁茂的天空岛Kaibab高原上。我们使用信息理论方法对代表替代假设的模型进行排名，这些假设关于降水的年度波动对苍鹰繁殖和雏鸟生产的年频率的影响。我们研究了125个苍鹰繁殖地区，²学习区。人口的主要人口统计特征是育种的年度广泛变化，表现为产卵对的比例，育雏尺寸，产蛋失败率和雏鸡生产的年际变化较大。上一年已知的当年产卵的地区的百分比范围为8％至86％（ = 37％，SE = 4.51），年平均巢蛋失败率（活动巢蛋失败）范围为12％到48％（总体 = 23％，SE = 2.48），并且成功筑巢的平均年孵尺寸（刚孵出的≥1个雏鸟）从1.5幼到2.5幼（总体 = 2.0年轻，SE = 0.03）。繁殖的年际变化密切跟踪降水的年际变化，我们假设这影响了原始森林的生产力以及鸟类和哺乳动物的猎物丰富度。最佳繁殖年（1992-1993年，成对产卵的77-87％）与创纪录的厄尔尼诺-南方涛动（ENSO）湿润时期和最差繁殖年（2003年；成对产卵的8％）相吻合。是三年来创纪录的干旱中的最后一次。总体育种成功率为83％，大多数失败发生在孵化过程中。一旦卵孵化，苍鹰就倾向于年轻。合并的20年雏巢性别比与众不同（53％M; n = 410 M，366 F），但在2年内明显偏向男性，在1年内明显偏向女性。尽管如此，在其他苍鹰种群中，雄性雏鸟的总体产量也出现了较大的增长趋势，这表明育种家可能已经在适应性地调整其后代性别比例，也许是为了生产更多的稀有（雄性）性别。在研究期间，每年平均有43％的新个体进入育种种群。当地出生的鹰的研究区域招募率（原位），条纹为0.12。两性返回凯巴布高原进行繁殖的趋势相同（哲学上没有差异），并且两性之间的出生扩散距离（从出生到第一个繁殖地点）也没有差异。在研究的最后几年（1999-2010年），估计有46％的新兵是在当地出生的，而54％是来自遥远森林的移民。首次育种的最小年龄为2岁，已知年龄的雄鹰（在初次繁殖时被绑成雏鸟或以羽毛成年的年龄）首次育种的平均年龄为雄性3.7岁，雌性为3.5岁。已知年龄的苍鹰的平均寿命（从第一次成群结巢到最后一次观察）的平均年龄为6.9年。基于首次捕获的羽毛，≥4岁的育种者的平均最低表观寿命为6.5岁。首次发现苍鹰的平均年龄为3.9岁，当时男女的表观存活率估计为0.77，仅略低于年龄随年龄变化的最高存活率0.78。特定年龄的生存估计显示9岁以后稳步下降，而20岁时接近0。繁殖成年动物的λ估计值（M，0.94，SE = 0.037； F，0.98，SE = 0.038）仅提供了在研究期间种群减少的微弱证据。尽管性别不在最佳的生存模型中，但包括年龄+性别在内的模型却具有竞争性，表明男性的生存率低于女性的生存率，这一发现与顶级λ模型中发生的性别效应相符。雄性成年觅食者在漫长的繁殖季节中，在植被茂密的环境中猎捕敏捷猎物会导致更高的死亡率，从而导致男性存活率降低。较低的存活率可以由雄性幼雏的更频繁生产（53％）来弥补。高强度冠冕之火是对人口的生存威胁。在1991年之前的30年中，除了发生了4次大火，烧毁了大约3,770公顷（相当于3个苍鹰领土），在我们的研究中，发生了6次大火，烧毁了另外30,945公顷，并杀死了大部分（> 64％）在我们完成调查之前，有8个已知地区的森林，还有可能还有2个被烧毁。高强度冠冕之火是对人口的生存威胁。在1991年之前的30年中，除了发生了4次大火，烧毁了大约3,770公顷（相当于3个苍鹰领土），在我们的研究中，发生了6次大火，烧毁了另外30,945公顷，并杀死了大部分（> 64％）在我们完成调查之前，有8个已知地区的森林，还有可能还有2个被烧毁。高强度冠冕之火是对人口的生存威胁。在1991年之前的30年中，除了发生了4次大火，烧毁了大约3,770公顷（相当于3个苍鹰领土），在我们的研究中，发生了6次大火，烧毁了另外30,945公顷，并杀死了大部分（> 64％）在我们完成调查之前，有8个已知地区的森林，还有可能还有2个被烧毁。